While only a couple of events in the third gravitational-wave transient catalog individually feature confidently high spin magnitudes or anti-alignment (i.e. a spin vector pointing opposite the angular momentum), hierarchically combining observations of GW events while folding in selection effects can reveal the degree to which these parts of spin parameter space contribute to the astrophysical distribution of BH spins. Previous work has used these inferred contributions to estimate the fraction of BBH systems in the local Universe which may have been formed hierarchically, dynamically, and by isolated evolution [1]}, [2]}, [3]}, [4]}. However, recent publications have disagreeing estimates for the contributions of anti-aligned and non-spinning BBHs to the astrophysical population.
